Recovering Projective Transformations between Binary Shapes

Binary image registration has been addressed by many authors recently however most of the proposed approaches are restricted to affine transformations. In this paper a novel approach is proposed to estimate the parameters of a general projective transformation (also called homography) that aligns two shapes. Recovering such projective transformations is a fundamental problem in computer vision with various applications. While classical approaches rely on established point correspondences the proposed solution does not need any feature extraction, it works only with the coordinates of the foreground pixels. The twostep method first estimates the perspective distortion independently of the affine part of the transformation which is recovered in the second step. As experiments on synthetic as well on real images show that the proposed method less sensitive to the strength of the deformation than other solutions. The efficiency of the method has also been demonstrated on the traffic sign matching problem.